Motion onset VEPs were recorded from human subjects using achromatic and chromatic stimuli. Ar low speeds (1 and 2 csec(-1)) and low contrasts ( 0.25), there were marked differences between the latencies and amplitudes of the chromatic and luminance motion onset responses. At higher speeds (10 csec(-1)) and higher contrasts, differences between the chromatic and achromatic VEPs were not as pronounced. The differences in VEP response behavior support the view that at low speeds there are separate channels for the processing of motion defined by colour and that defined by luminance, with the parvocellular and magnocellular systems as their respective neural substrates. The similarity that exists between achromatic and chromatic responses at higher speeds is suggestive of a single mechanism that encodes both colour and luminance, which is likely to be magnocellular in origin. (C) 2000 John Wiley & Sons, Inc.